1. Field of the Invention
The present invention relates generally to a method and apparatus for transmitting/receiving a data control channel in a packet data communication system, and in particular, to a method and apparatus for transmitting/receiving a data control channel for transmitting Persistent Resource Allocation information.
2. Description of the Related Art
In a conventional packet data communication system, a resource allocation scheme is classified into a Persistent and a Non-Persistent Resource Allocation scheme. The ‘resource’ is subject to change according to type of the communication system. For example, the resources can be codes in a Code Division Multiple Access (CDMA) system, frequency bands in a Frequency Division Multiple Access (FDMA) system, sub-carriers in an Orthogonal Frequency Division Multiple Access (OFDMA) system and time slots in a Time Division Multiple Access (TDMA) system.
Of the resources, the sub-carriers belong to frequency. In the following description, therefore, both the sub-carrier resources and the frequency band resources will be referred to as “frequency resources.” There can be a possible communication system supporting all of CDMA, FDMA, OFDMA and TDMA. In this case, the resources can include all of the codes, frequencies and time slots. In the following description, therefore, the resources can include all or some of the codes, sub-carriers and time slots, and this is subject to change according to the system.
Generally, the Persistent Resource Allocation scheme regards persistent allocation of an amount of Persistent Resource Allocation resources to one user, which resources are generally persistently valid unless the scheme newly changes the resources once allocated by a base station. However, the Non-Persistent Resource Allocation scheme regards a new allocation of resources per time slot or per a number of time slots.
FIG. 1 illustrates a conventional Persistent Resource Allocation scheme and Non-Persistent Resource Allocation scheme.
Referring to FIG. 1, the horizontal axis indicates time resources, and the vertical axis indicates frequency or code resources. Therefore, in the system shown in FIG. 1, the resources include frequencies, codes and time slots. That is, the system in FIG. 1 can be a system that allocates the frequency or code resources indicated by the vertical axis and the time slot resources indicated by the horizontal axis to different users every time slot 101. In FIG. 1, a data channel 102 indicates a physical channel for transmitting user data, and a data control channel 103 indicates a physical channel for transmitting control information necessary for data demodulation.
Generally, the data control channel 103 is referred to as, for example, Shared Control CHannel (SCCH), Data Control CHannel (DCCH) or Shared Signaling CHannel (SSCH), according to system. The data control channel serves to provide scheduling information to terminals, data transmission or resource allocation to which is scheduled, for every time slot interval. That is, all terminals in the system can receive the data control channel transmitted from the base station every slot, detect terminal identifier information included in the data control channel, and determine whether there are resources allocated to them by checking whether the detected terminal identifier information is equal to their own terminal identifier information.
The data control channel 103 can include various control information as well as the terminal identifier information according to other uses. However, because this is not related to the present invention, a detailed description thereof will be omitted. Although the resources over which the data channel 102 is transmitted and the resources over which the data control channel 103 is transmitted are divided on the vertical axis in FIG. 1 for convenience, it is not necessary that the resources be divided in this manner. In addition, numerals shown in the time axis of FIG. 1 indicate indexes 104 for time slots.
The Persistent Resource Allocation and Non-Persistent Resource Allocation schemes will now be described in detail with reference to FIG. 1. Numerals ‘1’ to ‘5’ in the shaded boxes are for user identification. It is assumed herein that Persistent Resource Allocation is performed for the users indicated by ‘1’, and Non-Persistent Resource Allocation is performed on the other parts (users) indicated by ‘2’ to ‘5’. On this assumption, for the parts indicated by ‘1’, Persistent Resource Allocation resources are allocated to the corresponding user and the data control channel 103 is transmitted together with data transmission at a time slot #1. In addition, the data control channel 103 transmitted at the time slot #1 includes not only the terminal identifier of the corresponding user, but also the information indicating Persistent Resource Allocation. For example, 1 bit is used herein for the information indicating Persistent Resource Allocation (hereinafter indication bit). Herein, indication bit=‘1’ indicates Persistent Resource Allocation, and indication bit=‘0’ indicates Non-Persistent Resource Allocation. All terminals in the system can detect the terminal identifier and the indication bit indicating Persistent Resource Allocation by receiving and demodulating the data control channel 103 transmitted at the time slot #1.
The terminals determine whether a terminal identifier received over the data control channel 103 is equal to their own terminal identifiers. Because the terminal identifier included in the data control channel 103 at the time slot #1 is a terminal identifier of the user indicated by, for example, ‘1’, terminals of the users indicated by the other terminal identifiers ‘2’ to ‘5’ except for the corresponding terminal identifier go to the next time slot, considering that there is no resource allocated to them.
However, the user indicated by ‘1’ recognizes that there are resources allocated to him/her, because his/her own terminal identifier has been received. The user then determines whether the resources allocated at this time are Persistent Resource Allocation resources or Non-Persistent Resource Allocation resources depending on an indication bit for Persistent Resource Allocation (hereinafter Persistent Resource Allocation indication bit). Because the Persistent Resource Allocation indication bit transmitted at time slot #1 is ‘1’, the terminal can recognize that the resources allocated at time slot #1 are Persistent Resource Allocation resources allocated to the terminal itself. Although only one code or frequency resource is allocated to data channel 102 in FIG. 1 for convenience, it should be noted that multiple code resources and frequency resources are actually allocated.
Therefore, the data control channel 103 generally includes information indicating the amount of allocated resources. The Persistent Resource Allocation resources allocated at time slot #1 include code or frequency resources and time slot resources. That is, the data control channel 103 includes information indicating which code or frequency resources it will allocate on a Persistent Resource Allocation basis per number of time slots. It is assumed in FIG. 1 that Persistent Resource Allocation resources are allocated to the user indicated by ‘1’ at the time slot #1 in the time axis every four time slots. Therefore, in the example of FIG. 1, the Persistent Resource Allocation resources for the user indicated by ‘1’ are applied to time slots #1, #5, #9, #13, etc.
An example of Non-Persistent Resource Allocation will now be described. It can be noted that a data channel 102 and a data control channel 103 are transmitted at a time slot #2. The data control channel 103 includes a terminal identifier for the user indicated by ‘2’ and a Persistent Resource Allocation indication bit=‘0’. Therefore, a base station transmits data to the user indicated by ‘2’ over the data channel 102, together with the data control channel 103. The resources allocated at the corresponding time slot are Non-Persistent Resource Allocation resources, and therefore is resource allocation applied only to the corresponding time slot.
Similarly, it can be noted in FIG. 1 that a data channel 102 and a data control channel 103 are retransmitted at a time slot #3. The data control channel 103 includes a terminal identifier for the user indicated by ‘3’ and Persistent Resource Allocation indication bit=‘0’. Therefore, the base station transmits data to the user indicated by ‘3’ over the data channel 102, together with the data control channel 103. That is, Non-Persistent Resource Allocation is applied only to the time slot. As time passes in the time slots #4, #5, #6, . . . , the base station continues to perform Persistent Resource Allocation or Non-Persistent Resource Allocation per time slot.
As described above, in the example of FIG. 1, the resources of the time slots #1, #5, #9, #13, . . . are Persistent Resource Allocation resources allocated to the user indicated by ‘1’, and the other resources except for the Persistent Resource Allocation resources are allocated as Non-Persistent Resource Allocation resources. As for the Persistent Resource Allocation, it should be noted that the data control channel 103 is generally transmitted only for initial Persistent Resource Allocation as shown in FIG. 1. That is, after signaling to the terminal the information indicating that specific resources are allocated on a Persistent Resource Allocation basis, the base station does not transmit a data control channel unless it intends to release the previously allocated Persistent Resource Allocation resources or it intends to change the amount or positions of the Persistent Resource Allocation resources. This is an important difference from Non-Persistent Resource Allocation, and can be verified through FIG. 1. That is, in FIG. 1, as to the time slots #1, #5, #9, #13, . . . , the data control channel is transmitted only at the first time slot #1, and the data control channel is no longer transmitted to the corresponding user (see reference numerals 111, 113 and 115). However, the data control channel is transmitted together with the data channel at all the other time slots, i.e. the time slots where Non-Persistent Resource Allocation is performed.
Therefore, it can be noted that a data control channel used for transmitting Persistent Resource Allocation information is much more important than a data control channel used for Non-Persistent Resource Allocation information. If a data control channel over which Persistent Resource Allocation information is transmitted suffers from an error in a transmission process, an influence of the error continues, greatly affecting the entire system performance. However, in the conventional communication system, the data control channel for transmitting Persistent Resource Allocation information and the data control channel for transmitting Non-Persistent Resource Allocation information are equal in transmission/reception structure and process, thereby causing a reduction in reception reliability of the data control channel for transmitting Persistent Resource Allocation information.